西亚试剂：Four amino acids guide the assembly or disassembly of Arabi

Four amino acids guide the assembly or disassembly of Arabidopsis histone H3.3-containing nucleosomes

Shi, Leilei; Wang, Jing; Hong, Fang; Spector, David L.; Fang, Yuda

The histone variant H3.3 and the canonical histone H3.1, which differ in only 4- to 5-aa positions, are coexpressed in complexmulticellular eukaryotes from fly to human and plant. H3.3 is mainly associated with active chromatin by replacing H3.1 throughchaperones such as histone regulator A, death domain associated protein DAXX, thalassemia/mental retardation syndrome X-linkedhomolog ATRX, or proto-oncogene protein DEK and plays important roles in the germline, epigenetic memory, and reprogramming.However, the signals within H3.3 that serve as a guide for its dynamic deposition or depletion in plant chromatin are notclear. Here, we show that Arabidopsis histone H3.3 differs from H3.1 by 4-aa sites: amino acids 31, 41, 87, and 90. Although histone H3.1 is highly enriched inchromocenters, H3.3 is present in nucleolar foci in addition to being diffusely distributed in the nucleoplasm. We have evaluatedthe function of the 4 aa that differ between H3.1 and H3.3. We show that amino acid residue 87, and to some extent residue90, of Arabidopsis histone H3.3 are critical for its deposition into rDNA arrays. When RNA polymerase I-directed nucleolar transcription isinhibited, wild type H3.3, but not H3.3 containing mutations at residues 31 and 41, is depleted from the rDNA arrays. Together,our results are consistent with a model in which amino acids 87 and 90 in the core domain of H3.3 guide nucleosome assembly,whereas amino acids 31 and 41 in the N-terminal tail of Arabidopsis H3.3 guide nucleosome disassembly in nucleolar rDNA.